"Nereus helped us explore places we've never seen before and ask questions we never thought to ask," said Timothy Shank of the Woods Hole Oceanographic Institution, the Massachusetts-based organization in charge of the sub's management.

"It was a one-of-a-kind vehicle that even during its brief life brought us amazing insights into the unexplored deep ocean, addressing some of the most fundamental scientific problems of our time about life on Earth," he continued.

The 6-year-old, $8 million remotely operated vehicle was lost Friday night during a dive 6.2 miles beneath the sea off the coast of New Zealand. Researchers later found debris floating on the surface, leading them to conclude the sub imploded under the immense weight of the ocean.

Nereus was on day 30 of a 40-day exploration of the Kermadec Trench, which lies at 32,963 feet below the surface of the sea. It's the world's second-deepest trench, second only to the Mariana Trench at 36,201 feet, and was created by a process of subduction, wherein the Pacific tectonic plate is pushed beneath the Indo-Australian Plate.

On land, we humans experience about 15 pounds-per-square-inch (psi) of pressure from the weight of the atmosphere, and the Nereus was likely experiencing 16,000 psi when it imploded, according to LiveScience.com

"Extreme exploration of this kind is never without risk, and the unfortunate loss of Nereus only underscores the difficulty of working at such immense depths and pressures," said Larry Madin, WHOI director of research. "Fortunately, there was no human injury as a consequence of this loss."